Unquestionably, there is a need to provide efficient means for applying solar energy to an increasing number of human and industrial uses, as other energy sources are depleted or become prohibitively expensive. The application of solar energy to building heating and cooling requirements are typical of this need. Among other things, an effective solar energy system for use in buildings must be not only relatively inexpensive, but also reliable and maintainence-free for long periods of time. Considering solar energy system costs, moreover, an apparently small improvement in thermal efficiency for one system with respect to others will, over the anticipated life of the slightly more efficient system, give that product a marked technical and commercial advantage.
Through the years, a number of proposals for collecting solar heat and utilizing this heat to increase water temperature for household heating and similar purposes have been advanced. Representative of many of these proposals are the following United States patents:
U.S. Pat. No. 4,029,080 relies on translucent roof panels and convective air flow between the roof rafters to convey heat to a fluid-filled tube.
U.S. Pat. No. 4,003,365 shows a system for wetting a solar-exposed membrane in order to heat the wetting water. The water, warmed in this manner, is stored in a reservoir for subsequent use.
U.S. Pat. No. 3,893,508 relates to pre-stressed concrete walls that contain cooling and heating systems.
U.S. Pat. No. 3,207,211 describes heat absorbing tabs that are secured to an eaves trough for melting ice and slush in order to promote water discharge from the trough.
U.S. Pat. No. 1,473,018 discloses a heat absorbing plate and a number of passageways associated with the plate to enable fluid in these passageways to absorb heat from the plate.
U.S. Pat. No. 705,350 describes a pair of closely spaced plates that form a capillary tube in which the water that is to be heated is spread as a thin film.
In all of the patents summarized above, however, none suggest a relatively inexpensive method for making a tube in which heat is conducted with high thermal efficiency to the fluid within with sturdy, inexpensive apparatus that can be transported with ease from one construction site to another.